Operations on these types of characteristic problems of the spine frequently require the stabilization of a portion of the spinal tract so as to facilitate the fusion of two or more vertebrae into a single bone structure. This type of operation is frequently used for the correction of many pathological conditions of the vertebral column such as, for example, degenerative disc diseases, scoliosis, spinal stenosis or the like.
The stabilization of the vertebral column allows bone tissue to be created in the intervertebral area. In this way, part of the vertebral column is fused into a single bone structure. The stabilization of the vertebral column has been studied in the past and various methods and devices have been developed for the correction of many characteristic diseases of this part of the body, in order to stabilize its configuration, facilitating vertebral fusion at various levels.
One of these known systems envisions a corrective bar being arranged longitudinally along the spinal tract that requires surgery. This corrective bar is conformed so as to restore the correct anatomical shape, which is peculiar to that specific tract of a healthy vertebral column.
Therefore, with this method, the corrective bar is positioned along the vertebral column to engage various vertebrae, according to requirements. It should be noted that, typically, in this type of surgery two parallel corrective bars are arranged to the rear of the sides of the central area of the patient's vertebral column. Therefore, during the surgery, the pair of corrective bars is fixed to the vertebral column through various anchoring means including, for example, screws. The screws are fixed to the bone structure, typically to the vertebral peduncle.
The inclination of the corrective bar and, consequently, the positioning of the set screws, vary according to the type of correction to be made and, naturally, vary from vertebra to vertebra. One type of screws known in the state of the art that are widely used in the application are polyaxial screws. Here, the head of the screw can vary its angulation with respect to the threaded stem for better adaptation to the surgical requirements until a set screw is coupled to it.
It appears clear how it is fundamental, for a successful operation, to correctly fix both the corrective bar and the screws to which it will be fixed. In fact, the corrective bar is inserted into a head of the polyaxial screw and secured thereto through the fixing of a set screw, coupled by means of a helical coupling so that, once the coupling is complete, the set screw is locked in the desired position and the corrective bar is fixed into the housing provided in the screw head. Therefore, until the set screw is correctly coupled, the head of the polyaxial screw is free to move.
In typical approaches, instruments are known for the coupling of a set screw with a head of a polyaxial screw. The fixing instruments can be likened to screwdrivers through which it is possible to act on the set screw to create the threaded coupling between it and the head of the polyaxial screw. In fact, through the coupling, the set screw drops into the head of the polyaxial screw until it presses against a corrective bar and stops against it. In this way, the corrective bar is controlled to press against the spherical end of the threaded stem of the polyaxial screw, which is also contained in the head of the screw. In this way, the spherical end of the stem of the polyaxial screw and the bar are locked in the desired position.